The invention relates to the field of removing particles in the range of about 10 microns (diameter) or less from fluid streams. This removal from air streams is typically done now with bag houses or electrostatic precipitators and from liquids with screens or filters. Bag houses usually employ fabrics which serve as the support for the buildup of a filter cake. Periodically, the filter cake is shaken or blown loose from the fabric and collected, and the cycle repeated. The filter cake is essentially a buildup of dust dendrites which provide the surface area for collection of submicron particles. Typical pressure drops are on the order of 16 cm W. C. (water column). As might be expected, there is some loss of efficiency after the cake is removed during the cleaning cycle and there tends to be a relatively high pressure drop during the latter phase of filtration just prior to cleaning. Furthermore, bag house fabrics may blind due to lodging of fine particles or sticky materials in the pores of the fabric.
In addition to commercial bag houses and electrostatic precipators, research and development work has been done on recirculating, granular-bed filters. These filters comprise a bed of granules in which the granules are recycled out the bottom of the bed, cleaned and returned to the top. Dirty gas flows from side to side or from bottom to top (counter-current to the granule movement).
The present nested-fiber bed is distinguished from the granule bed by its ability to nest the fibers in a controlled way to promote dendritic buildup of particles necessary to filter efficiently. The high voidage of the nest permits higher dust loading and higher efficiency at constant pressure drop. Moreover, the fibers and dirty fluid move in a co-current manner without disrupting the dendrites. Rolling motion in the granular bed tends to disrupt previously formed dendrites, thus reducing efficiency.